1. Field of the Invention
The present invention relates to an image forming apparatus capable of recycling residual toner on the photosensitive drum surface after forming an image in an image forming method such as electrophotography. More specifically, the invention relates to an image forming apparatus, in which recovered toner is not used as it is, but its external additive concentration is returned to an appropriate level to turn it into recycled toner with the same properties as fresh toner, and recycle this recycled toner.
2. Description of the Related Art
Conventionally, image forming apparatuses using electrophotography are widely used. In electrophotography, an electrostatic latent image, which has been formed on the surface of a photosensitive drum serving as an electrostatic latent image carrier, is developed with toner, transferred onto a sheet of recording paper or the like and ejected. In such an apparatus, the toner on the photosensitive drum is not necessarily transferred entirely to the sheet, and some of it remains on the surface of the photosensitive drum. After the residual toner that has remained on the photosensitive drum has been removed in a cleaning step, it is recovered in a toner container, such as a toner bottle, and disposed of. That is to say, in conventional methods, recovered toner is not recycled.
In recent years, image forming apparatuses have become much faster, and the number of images printed per unit time has grown very high, so that also the amount of residual toner has grown to large quantities. The principle component of the residual toner is a binder resin, and disposing large quantities thereof may lead to environmental pollution.
Under these circumstances, there has been much talk in recent years about pollution of the environment and the efficient use of natural resources, so that a strong demand for the recycling of residual toner in image forming apparatuses has developed.
One method that is used for this is to supply the toner that has been eliminated or recovered in a cleaning step as it is to a developing unit via conveying means.
FIGS. 15A and 15B show a conventional image forming apparatus 200 that can recycle residual toner. FIG. 15A shows the general configuration of this conventional image forming apparatus 200, which can recycle residual toner. FIG. 15B is a magnification showing the general configuration of the image forming portion of the image forming apparatus 200 shown in FIG. 15A.
The image forming portion of the image forming apparatus 200 includes a charging unit 202, an exposure device 203, a developing unit 204, a transfer device 205, a peel-off device 208, a cleaning device 206, and a discharger 207 arranged around a rotatable cylindrical photosensitive drum 201 serving as an electrostatic latent image carrier and having an organic photoconducting photosensitive layer, as well as a toner recycling portion 209, which conveys the residual toner that has been recovered with the cleaning device 206 to the developing unit 204.
The image formation is carried out in the following order. To carry out an image formation, the photosensitive drum 201 is first rotated in the arrow direction A, and the surface of the photosensitive drum 201 is charged uniformly with the charging unit 202. Then, the exposure device 203 exposes photosensitive drum 201 in correspondence with the original document. This forms on the surface of the photosensitive drum 201 an electrostatic latent image corresponding to the original document. In the developing unit 204, this electrostatic image is made visible by supplying toner with a developing roller 204d. The toner image is transferred by the transfer device 205 onto a transfer material, such as a piece of paper, which has been conveyed from a paper feed portion 210. After the transfer material, onto which the toner has been transferred, has been subjected to a fixing process with the fixing device 211, it is ejected out of the image forming apparatus.
After the transfer step, the residual toner that has remained on the surface is scraped off the photosensitive drum 201 with a cleaning blade 206a of the cleaning device 206, and the charge on the surface of the photosensitive drum 201 is eliminated with the discharger 207. Then, the surface of the photosensitive drum 201 is uniformly charged again with the cleaning unit 202, and the above steps are repeated.
The residual toner that has been recovered by the cleaning device 206 is conveyed through the toner recycling portion 209, which is provided with a screw, to the developing unit 204, is mixed with the toner that has accumulated in the developing unit 204 while being stirred, and is used again for making electrostatic latent images on the photosensitive drum 201 visible. The replenishing of fresh toner is performed from a toner cartridge 212, serving as a toner supply portion, provided at the top of the developing unit 204.
In the above-described series of image forming steps, matter generated by the corona charging and foreign matter, such as paper particles or talc, which is contained in the paper sheets or other transfer material, adheres to the surface of the photosensitive drum 201, in addition to the residual toner. In the image forming apparatus shown in FIGS. 15A and 15B, if foreign matter, such as particles of the paper sheets or toner coagulates, is conveyed through the toner recycling portion 209 to the developing unit 204 together with the toner, then this may adversely influence the following image forming steps, and when foreign matter is supplied together with the toner to the surface of the photosensitive drum 201, a decline of the image quality, such as blank spots in the image, may occur. There is also the possibility that the surface of the photosensitive drum 201 is damaged. Consequently, to recycle the residual toner that has been recovered, it was necessary to recycle the residual toner by some means.
A technique that has been proposed to solve this problem is to carry out a recycling process, in which the recovered toner is passed through a lattice-shaped filter (mesh), and foreign matter mixed into the recovered toner is eliminated, as for example in the image forming -method disclosed in Japanese Unexamined Patent Publication JP-A 8-185101 (1996). This technique also carries out a process in which the separatability of the foreign matter from the recovered toner is improved. With this technique, it is possible to obtain a recycled toner that can maintain a high image density from beginning to end, and without covering of the document with toner and toner scattering.
In the toner cartridge disclosed in Japanese Unexamined Patent Publication JP-A 6-130810 (1994), a residual toner storage tank for collecting residual toner is coupled to and formed in one piece with a fresh toner storage tank for supplying fresh toner to the developing unit. The residual toner is mixed with the fresh toner, and this toner mixture of residual toner and fresh toner is supplied to the developing unit via a conveyance duct, and thereby recycled. A wall in which holes with small diameter are formed or a lattice-shaped wall is provided between the residual toner storage tank and the fresh toner storage tank, which prevents that foreign matter or residual toner particles with large particle diameter are transferred to the fresh toner storage tank. Furthermore, this cartridge also improves the conveyability and the chargeability of the residual toner by mixing the fresh toner and the residual toner while stirring.
Although this toner cartridge improves the properties of the residual toner, the properties of the fresh toner, which is mixed with the residual toner, deteriorate. Therefore, it cannot provide a mixed toner of high quality. The reason for this is that not only are impurities mixed into the recovered residual toner, but the composition of the toner itself changes. That is to say, the residual toner""s conveyability (flow properties) and the chargeability (ability to be charged by friction) worsen due to this composition change. Therefore, it is not possible to form a high-quality image just by eliminating the foreign matter.
To solve this problem, the previously mentioned JP-A 8-185101 discloses a toner recycling method, in which the recovered residual toner is passed through a lattice-shaped filter (mesh), impurities are eliminated, and the flowability index is decreased to 70 or less by adding a halide of an azo iron complex to the recycled toner.
However, this addition process is not a recycle process by which the composition of the toner is restored, so that a recycled toner of sufficient quality cannot be attained. Furthermore, a maximum of 20 parts by weight of the halide of an azo iron complex are added to 100 parts by weight of the toner, which is not practical with regard to costs. Also, in an image forming apparatus using this addition process, the separation device serving as the component for recycling the residual toner has a complicated structure. Therefore, the steps for manufacturing the image forming apparatus become complicated, and the number of parts increases, so that the manufacturing costs rise.
On the other hand, the configuration of the toner cartridge disclosed in JP-A 6-130810 focuses only on the recycling of recovered residual toner, so that the worsening of the properties of fresh toner due to the mixing with residual toner is not considered. That is to say, the residual toner is transferred directly into the fresh toner storage tank and mixed, so that it is not possible to control the mixing ratio of residual toner and fresh toner. Therefore, for example at the beginning of the image formation, the mixing ratio of residual toner to fresh toner is low, so that a favorable image quality can be attained, but if image formation is repeated without replenishing fresh toner, the mixing ratio of residual toner to fresh toner gradually becomes high, and the image quality tends to worsen. Especially when printing large amounts of black beta images with high text density, large amounts of the toner mixture of fresh toner and residual toner are consumed, and as a result, large amounts of the residual toner are recovered and mixed again, so that the above problems are even more pronounced.
It is an object of the invention to solve these problems and to provide an image forming apparatus in which recycled toner with high quality can be produced from residual toner and reused.
The invention provides an image forming apparatus comprising a developing unit for supplying toner to an electrostatic latent image formed on an electrostatic latent image carrier and making the electrostatic latent image visible; a transfer device for transferring the toner image made visible onto a transfer material; a cleaning device for eliminating and collecting residual toner remaining on the electrostatic latent image carrier after transferring the toner image; a conveyor device for conveying residual toner that has been collected by the cleaning device, to the developing unit; and a toner recycling portion for producing recycled toner by supplementing an external additive to the collected residual toner conveyed to the developing unit, wherein the resulting recycled toner is reused for image formation.
According to the invention, the residual toner that has been eliminated and collected with the cleaning device is conveyed to the developing unit with the conveyor device, and the image forming apparatus is provided with the toner recycling portion for producing recycled toner by supplementing an external additive to the collected residual toner. Consequently, the amount of external additive contained in the collected residual toner is substantially the same as in fresh toner, which improves the charge stability, developing properties, flow properties and durability of the recycled toner. Moreover, with the recycled toner produced with this image forming apparatus, an image formation can be realized that is substantially as reliable as with fresh toner.
In another aspect of the invention, the external additive is a powder of at least one of silica, alumina and titania.
In accordance with this aspect of the invention, the recycled toner is produced by adding to the collected residual toner at least one powder of silica, alumina and titania as an external additive. Consequently, the residual toner can be recycled easily, because these powders are regular materials that are easy to acquire.
In another aspect of the invention, an amount of the external additive which is supplemented to the collected residual toner in the toner recycling portion satisfies the following equation:
0.9Yxe2x88x92Xxe2x89xa6Zxe2x89xa61.1Yxe2x88x92X
wherein Y[% by weight] is weight ratio of external additive contained in fresh toner, and X[% by weight] is weight ratio of external additive contained in the collected residual toner, and Z [% by weight] is weight ratio of the external additive to be supplemented to the collected residual toner.
In accordance with this aspect of the invention, the amount of the external additive to be supplemented to the collected residual toner can be set to be within xc2x110% of that included in fresh toner. Thus, the composition of the recycled toner can be restored favorably, and it is possible to produce toner of a quality that is substantially the same as that of fresh toner.
In another aspect of the invention, the toner recycling portion includes foreign matter eliminating means for eliminating foreign matter that is contained in the collected residual toner.
In accordance with this aspect of the invention, the toner recycling portion includes the foreign matter eliminating means for eliminating foreign matter that is contained in the collected residual toner. Consequently, it is possible to prevent image deficiencies and damage to the photosensitive drum surface.
In another aspect of the invention, the foreign matter eliminating means is cup-shaped, at least a bottom portion of the foreign matter eliminating means is made of a mesh, and the foreign matter eliminating means is provided detachably in an aperture portion of the toner recycling portion.
In accordance with this aspect of the invention, at least the bottom portion of the foreign matter eliminating means is made of a mesh, and the foreign matter eliminating means is detachable. Consequently, foreign matter contained in the collected residual toner can be eliminated easily before the recycled toner is produced in the toner recycling portion. Furthermore, the foreign matter that has accumulated in the foreign matter eliminating means can be removed easily and reliably.
In another aspect of the invention, a size of holes in the mesh of the foreign matter eliminating means is larger than a diameter of residual toner particles to be recycled and smaller than a particle diameter of the foreign matter to be eliminated.
In accordance with this aspect of the invention, the size of the holes in the mesh provided at the bottom portion of the foreign matter eliminating means is smaller than the particle diameter of the foreign matter to be eliminated and collected and larger than the diameter of the residual toner particles to be recycled. Thus, the foreign matter can be reliably separated and eliminated from the collected residual toner reliably, and the clogging of the mesh with residual toner can be avoided.
In another aspect of the invention, the toner recycling portion includes a collected residual toner storage for storing collected residual toner; an external additive cartridge for storing the external additive; and a connection portion connecting the collected residual toner storage and the external additive cartridge.
In accordance with this aspect of the invention, the external additive cartridge is connected to the collected residual toner storage through the connection portion. Consequently, the external additive stored in the external additive cartridge can be supplied easily through the connection portion to the collected residual toner storage.
In another aspect of the invention, the external additive cartridge is attached detachably to a top of the collected residual toner storage.
In accordance with this aspect of the invention, the external additive cartridge is attached detachably to the collected residual toner storage. Consequently, the external additive cartridge can be exchanged easily after the addition of external additive.
In another aspect of the invention, the external additive cartridge is provided with an aperture portion sealed with a heat seal, which connects the external additive cartridge with the collected residual toner storage when the heat seal is removed.
In accordance with this aspect of the invention, the aperture portion of the external additive cartridge storing the external additive is sealed with a heat seal, so that external additive does not spill out, and when the heat seal is removed, the aperture portion connects the external additive cartridge with the collected residual toner storage. Consequently, users can supply external additive to the collected residual toner storage easily without making their hands dirty by removing the heat seal. Furthermore, with this configuration, a used up empty cartridge or a new external additive cartridge that has been substituted can be used with the lid of the collected residual toner storage.
In another aspect of the invention, the collected residual toner storage includes stirring means for stirring the collected residual toner and the external additive.
In accordance with this aspect of the invention, the collected residual toner storage includes stirring means for stirring the collected residual toner and the external additive. Consequently, it is easy to produce recycled toner whose properties are the same as those of fresh toner by stirring the external additive supplied to the collected residual toner storage and the collected residual toner collected from the electrostatic latent image carrier with the stirring means.
In another aspect of the invention, the image forming apparatus further comprises collected residual toner detection means for detecting an amount of toner in the collected residual toner storage; and notification means for notifying, when the amount of toner detected by the collected residual toner detection means has reached an amount equal to or larger than a first predetermined amount.
In accordance with this aspect of the invention, the amount of collected residual toner in the collected residual toner storage is detected with the collected residual toner detection means, and when this amount of toner is equal to or larger than a first predetermined amount, the user is notified of the fact that this amount of toner is equal to or larger than the first predetermined amount. Consequently, the user can easily confirm that the amount of collected residual toner that has been collected has reached the first predetermined amount. This makes it easy to produce recycled toner of an appropriate composition, and prevents the deterioration of the quality of the recycled toner.
In another aspect of the invention, the image forming apparatus further comprises control means for stopping image formation when the toner amount detected by the collected residual toner detection means has reached a second predetermined amount.
In accordance with this aspect of the invention, the image formation is stopped when the collected residual toner has reached the second predetermined amount. Thus, it is possible to strongly urge the user to produce recycled toner when the user has forgotten to supply external additive, to prevent the collected residual toner from exceeding the second predetermined amount, and to reliably produce recycled toner of an appropriate composition.
In another aspect of the invention, the toner recycling portion includes a fresh toner storage in which recycled toner is mixed with fresh toner; and a connection portion for connecting the fresh toner storage with the collected residual toner storage.
In accordance with this aspect of the invention, the fresh toner storage is connected by the connection portion with the collected residual toner storage, to mix the fresh toner with recycled toner. Consequently, recycled toner is conveyed through the connection portion from the collected residual toner storage, and fresh toner is mixed before use with the recycled toner in the fresh toner storage, so that the image quality can be improved even more than using only recycled toner.
In another aspect of the invention, the fresh toner storage includes fresh toner detection means for detecting a toner amount, and notification means for notifying, when the amount of toner detected by the fresh toner detection means has decreased to an amount equal to or smaller than a predetermined amount, a user of the decrease.
In accordance with this aspect of the invention, when the fresh toner detection means has detected that the amount of toner in the fresh toner storage has decreased to an amount equal to or smaller than a predetermined amount, the notification means notifies the user of the decrease. Consequently, when the toner in the fresh toner storage used for developing is running short, the user can be urged to replenish fresh toner and a deterioration of the image quality due to toner shortage can be avoided.
Another image forming apparatus in accordance with the invention comprises a developing unit for supplying toner to an electrostatic latent image that has been formed on an electrostatic latent image carrier to form a toner image; a transfer device for transferring the toner image onto a transfer material; a cleaning device for eliminating and collecting residual toner remaining on a surface of the electrostatic latent image carrier after transferring the toner image; and a toner recycling portion for producing recycled toner by stirring collected residual toner that has been collected with the cleaning device and high concentration toner containing an external additive whose concentration is higher than that of fresh toner, wherein the collected residual toner is reused for image formation as recycled toner.
In an image forming apparatus in accordance with the invention, (i) residual toner that has remained on the surface of the electrostatic latent image carrier and eliminated and collected with the cleaning device and (ii) high concentration toner containing an external additive whose concentration is higher than that of fresh toner are mixed while being stirred in a toner recycling portion so as to produce recycled toner. Consequently, a concentration of external additive in a collected residual toner can be increased, and the collected residual toner with enhanced quality can be recycled.
In another aspect of the invention, the external additive is a powder of at least one of silica, alumina and titania.
In accordance with this aspect of the invention, at least one of silica, alumina and titania is added to the collected residual toner as an external additive. Consequently, the quality of the residual toner can be improved easily to reuse as recycled toner, because these powders are regular materials that are easy to acquire.
In another aspect of the invention, the external additive has a hydrophobicity of at least 40%.
In accordance with this aspect of the invention, the external additive, which is made of a powder of at least one of silica, alumina and titania, has a hydrophobization degree of at least 40%. Consequently, variations in the chargeability of the toner can be suppressed even under high temperatures and high humidities.
In another aspect of the invention, the foreign matter eliminating means is cup-shaped, at least a bottom portion of the foreign matter eliminating means is composed of a mesh, and a size of holes in the mesh is larger than a diameter of toner particles to be recycled and smaller than a particle diameter of the foreign matter to be eliminated.
In accordance with this aspect of the invention, the size of the holes in the mesh provided at the bottom portion of the foreign matter eliminating means is smaller than the particle diameter of the foreign matter to be eliminated and collected and larger than the diameter of the collected residual toner particles to be recycled. Thus, the foreign matter can be reliably separated and eliminated from the collected residual toner.
In another aspect of the invention, the foreign matter eliminating means includes foreign matter detection means for detecting an amount of matter collected in the foreign matter eliminating means; and notification means for notifying, when the amount of collected matter has reached a predetermined amount.
In accordance with this aspect of the invention, when the foreign matter detection means has detected that the amount of matter collected in the foreign matter eliminating means has reached a predetermined amount, then this fact is announced by the notification means. Consequently, the user of the image forming apparatus does not have to constantly check the amount of matter collected in the foreign matter eliminating means.
In another aspect of the invention, the foreign matter eliminating means includes foreign matter stirring means for stirring the matter collected in the foreign matter eliminating means.
In accordance with this aspect of the invention, foreign matter stirring means stirs the matter collected in the foreign matter eliminating means. Consequently, toner that can be recycled can be collected reliably, even when foreign matter and toner coagulations with large diameter have accumulated in the foreign matter eliminating means and toner that can be recycled adheres to the foreign matter, for example, because the collected residual toner is stirred when being passed through the foreign matter eliminating means.
In another aspect of the invention, the toner recycling portion includes a collected residual toner storage for storing collected residual toner; a high concentration toner accommodating portion for accommodating high concentration toner containing an external additive whose concentration is higher than that of fresh toner; a conveyance path for conveying collected residual toner from the collected residual toner storage to the high concentration toner accommodating portion; and stirring means for stirring toner in the high concentration toner accommodating portion.
In accordance with this aspect of the invention, collected residual toner that has accumulated in the collected residual toner storage is conveyed through the conveyance path to the high concentration toner accommodating portion, and the collected residual toner and the high concentration toner are stirred by the stirring means in the high concentration toner accommodating portion, which stores high concentration toner containing an external additive whose concentration is higher than that of fresh toner. Consequently, the collected residual toner and the high concentration toner are stirred in the high concentration toner accommodating portion to produce recycled toner, so that a recycled toner of high quality can be used to carry out the image formation.
In another aspect of the invention, the toner recycling portion includes a fresh toner storage for storing fresh toner; a conveyance path for conveying recycled toner from the high concentration toner accommodating portion to the fresh toner storage; and stirring means for stirring toner in the fresh toner storage.
In accordance with this aspect of the invention, recycled toner that has been produced in the high concentration toner accommodating portion is conveyed through the conveyance path to the fresh toner storage where fresh toner is stored, and the stirring means stirs the fresh toner and the recycled toner are stirred by the stirring means. Consequently, the image formation is carried out not only with recycled toner, but after stirring the recycled toner with fresh toner, so that images can be formed with even higher quality.
In another aspect of the invention, the collected residual toner storage includes toner detection means for detecting an amount of toner stored in the collected residual toner storage; and means for conveying toner that has been stored in the collected residual toner storage to the high concentration toner accommodating portion.
In accordance with this aspect of the invention, the collected residual toner storage is provided with the toner detection means for detecting an amount of toner that has been collected and the means for stirring and conveying toner that has been stored in the collected residual toner storage to the high concentration toner accommodating portion. Consequently, when the amount of toner stored in the collected residual toner storage reaches a predetermined amount, the toner can be conveyed to the high concentration toner accommodating portion.
In another aspect of the invention, the toner recycling portion includes a toner accommodating portion for accommodating high concentration toner containing an external additive whose concentration is higher than that of fresh toner; a conveyance path for conveying collected residual toner that has been collected with the cleaning device to the toner accommodating portion; and stirring means for stirring the toner in the toner accommodating portion.
In accordance with this aspect of the invention, the collected residual toner that has been collected with the cleaning device is conveyed through the conveyance path to the toner accommodating portion, which accommodates high concentration toner containing an external additive whose concentration is higher than that of fresh toner, where it is stirred with high concentration toner by the stirring means. Consequently, the collected residual toner and the high concentration toner are mixed in the toner accommodating portion, so that the quality of the collected residual toner is enhanced by increasing the concentration of external additive in the collected residual toner, and such quality-enhanced collected residual toner can be used for the developing. Moreover, the collected residual toner can be recycled in a device with simple configuration without providing a component for storing the collected residual toner.
In another aspect of the invention, the toner accommodating portion includes toner detection means for detecting an amount of toner accommodated by the toner accommodating portion, and means for conveying toner that is accommodated by the toner accommodating portion, to the fresh toner storage.
In accordance with this aspect of the invention, the toner accommodating portion is provided with the toner detection means for detecting an amount of toner accommodated therein, and the means for stirring and conveying collected residual toner stored in the collected residual toner storing portion to the toner accommodating portion. Consequently, toner is conveyed to the high concentration toner accommodating portion when the toner stored in the collected residual toner storage has reached a predetermined amount.
In another aspect of the invention, the fresh toner storage includes detection means for detecting an amount of toner stored in the fresh toner storage; and notification means for notifying, when the amount of toner has decreased to a predetermined amount.
In accordance with this aspect of the invention, when the detection means for detecting an amount of toner stored in the fresh toner storage detects that the amount of toner has decreased to a predetermined amount, then the user is notified of this fact. Consequently, when the toner used for developing runs short, the user can be urged to replenish fresh toner, so that a reliable image formation is possible even in the case of a toner shortage.